Little Boy Fissioned 1.7 Percent

On August 6, 1945, the uranium-based Little Boy atomic bomb detonated over Hiroshima, Japan, carrying about 64 kilograms of uranium-235. The reaction blew the bomb apart so quickly that only 1.7 percent of its material underwent nuclear fission. More than 98 percent remained unfissioned, yet the explosion still released energy equivalent to 15 to 16 kilotons of TNT.

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